#async-args

A utility for use in conjunction with async or similar libraries to help with passing and storing arguments between asynchronous functions.

Inspiration comes from:

• using async.waterfall which is shown in the examples.
• using async.constant and wanting more

This utility aspires to facilitate the following goals:

• Keep chained functions as generic as possible
  • Maximize reuse
  • Simpler to reason about
• Minimize defining functions within other functions:
  • Improve readability
  • Maximize reuse.

The disadvantage to these goals, similar to a microservices architecture, is that it pushes complexity to the integration layer. This library is intended to help manage that complexity.

Concepts

Think of async-args as a collection of factory functions which produce async functions to replace, select, or insert arguments. You can explore an interactive code example here.

API

Static Usage

• constants
• appendConstants
• prependConstants
• select
• order
• debug

Instance Usage
The same static methods as above are available, in addition to the following:

• store
• values
• appendValues
• prependValues

Static Usage

The static library is returned from the require statement

AsyncArgs = require('async-args')

The following methods are available:

###AsyncArgs.constants([constant], [constant], ...)

Pass constants as arguments to the adjoining function. Arguments from the preceding function are omitted. This method is equivalent to async.constant.

async.waterfall([
  AsyncArgs.constants('arg1'),  // (next)
  aFunctionTakingOneArg         // (arg1, next)
], next)

###AsyncArgs.appendConstants([constant], [constant], ...)

Append constants to the arguments coming from the preceding function.

async.waterfall([
  outputArg1,                         // (next)
  AsyncArgs.appendConstants('arg2'),  // (arg1, next)
  aFunctionTakingTwoArgs              // (arg1, arg2, next)
], next)

###AsyncArgs.prependConstants([constant], [constant], ...)

Prepend constants to the arguments coming from the preceding function

async.waterfall([
  outputArg1,                          // (next)
  AsyncArgs.prependConstants('arg2'),  // (arg1, next)
  aFunctionTakingTwoArgs               // (arg2, arg1, next)
], next)

###AsyncArgs.select([selector], [selector], ...])

selector: boolean, JSON Pointer or array of JSON Pointers

A selector can be a string, to select a subset of arguments coming from the preceding function.

async.waterfall([
  outputArg1Arg2Arg3,                    // (next)
  AsyncArgs.select(false, false, true),  // (arg1, arg2, arg3, next)
  aFunctionTakingOneArg                  // (arg3, next)
], next)

A selector can be a JSON Pointer, to select an array item or object property from an argument.

var constant = {a:{b:['c','d']}}
async.waterfall([
  AsyncArgs.constants(constant, constant), // (next)
  AsyncArgs.select('/a/b/1', /a/b/0'),     // (constant, constant, next)
  aFunctionTakingTwoArgs                   // ('d', 'c', next)
], next)

A selector can be an array of JSON Pointers, to select multiple array items or object properties from a single argument.

var constant = {a:{b:['c','d']}}
async.waterfall([
  AsyncArgs.constants(constant),          // (next)
  AsyncArgs.select(['/a/b/1', /a/b/0']),  // (constant, next)
  aFunctionTakingTwoArgs                  // ('d', 'c', next)
], next)

###AsyncArgs.order([integer], [integer], ...)

Change the order of the arguments.

async.waterfall([
  outputArg1Arg2Arg3,        // (next)
  AsyncArgs.order(2, 0, 1),  // (arg1, arg2, arg3, next)
  aFunctionTakingThreeArgs   // (arg3, arg1, arg2, next)
], next)

###AsyncArgs.debug([msg, [logger]])

msg: A string that replaces the default "AsyncArgs:" prefix
logger: A function taking msg as the first argument and args array as the second. The default is console.log.

Output what the current arguments are. All arguments pass through.

async.waterfall([
  outputArg1Arg2Arg3,  // (next)
  AsyncArgs.debug()    // (arg1, arg2, arg3, next)
], next)

// Output to console:
// AsyncArgs: [ 'arg1', 'arg2', 'arg3' ]

Instance Usage

An instance is returned by calling the static library, which allows the storing and retrieving of values from a context object.

var asyncArgs = AsyncArgs()

You can prepopulate the context object when the instance is first created:

var context = {
  'key1': 'value1',
  'key2': 'value2'
 }
var asyncArgs = AsyncArgs(context)

This context object is updated in place (no copy is made), so if you want synchronous access to these values, follow this example to reference the context for later use.

The same static methods as above are available, along with the following methods unique to instances:

###asyncArgs.store([key1], [key2], ...)

Store selected arguments coming from the previous function to the context object. Arguments from the preceding function pass through.

async.waterfall([
  outputArg1Arg2Arg3,                       // (next)
  asyncArgs.store('arg1', 'arg2', 'arg3'),  // (arg1, arg2, arg3, next)
  aFunctionTakingThreeArgs                  // (arg1, arg2, arg3, next)
], next)

###asyncArgs.values([key1], [key2], ...)

Pull specific values from the context object and pass as arguments to the adjoining function. Arguments from the preceding function are omitted.

async.waterfall([
  outputArg1Arg2Arg3,                       // (next)
  asyncArgs.store('arg1', 'arg2', 'arg3'),  // (arg1, arg2, arg3, next)
  aFunctionTakingThreeArgsAndOutputArg4,    // (arg1, arg2, arg3, next)
  asyncArgs.values('arg2'),                 // (arg4, next)
  aFunctionTakingOneArg                     // (arg2, next)     
], next)

###asyncArgs.appendValues([key1], [key2], ...)

Pull specific values from the context object and append to the arguments coming from the preceding function.

async.waterfall([
  outputArg1Arg2Arg3,                       // (next)
  asyncArgs.store('arg1', 'arg2', 'arg3'),  // (arg1, arg2, arg3, next)
  aFunctionTakingThreeArgsAndOutputArg4,    // (arg1, arg2, arg3, next)
  asyncArgs.appendValues('arg2'),           // (arg4, next)
  aFunctionTakingTwoArgs                    // (arg4, arg2, next)
], next)

###asyncArgs.prependValues([key1], [key2], ...)

Pull specific values from the context object and prepend to the arguments coming from the preceding function.

async.waterfall([
  outputArg1Arg2Arg3,                       // (next)
  asyncArgs.store('arg1', 'arg2', 'arg3'),  // (arg1, arg2, arg3, next)
  aFunctionTakingThreeArgsAndOutputArg4,    // (arg1, arg2, arg3, next)
  asyncArgs.prependValues('arg2'),          // (arg4, next)
  aFunctionTakingTwoArgs                    // (arg2, arg4, next)
], next)